1. Field of the Invention
This invention relates to a motor vehicle roof with a roof opening located in a fixed roof surface and a cover for closing the roof opening, the cover comprising at least one partially transparent pane and a frame which is connected to the pane and which extends over at least one part of the edge of the pane.
2. Description of Related Art
In these motor vehicles roofs, which can be roofs with a fixed or movable cover, the pane is conventionally a glass pane which is connected by means of a peripheral frame to the motor vehicle roof itself or to a positioning mechanism for positioning the cover. The frame can, moreover, be formed by foaming the pane in place, into which cover a metallic reinforcing or holding frame, for example, inner metal cover sheet, is inserted.
Aside from the glass elements, plastic panes which are cemented to a frame surrounding the pane are furthermore used in vehicle construction, especially for fixed elements.
While glass panes are advantageous in that they can be more easily worked, especially using techniques of foaming in place, it is however disadvantageous that glass covers have considerable inherent weight; this is disadvantageous not only with respect to the total weight of a roof structure, but especially when the cover is a movable cover which then requires a more complex configuration of the components supporting the cover and of the drive of the cover.
Plastic covers are lighter than glass covers, but much more difficult to install than the latter. This is due to the fact that the plastics used for producing vehicle roof covers generally have coefficients of thermal expansion which are very different from those of the metallic reinforcing and holding frame, and therefore, require corresponding movable connections between the pane and the frame, as is explained, for example, in German Patent DE 101 08 527 and corresponding U.S. Patent Application Publication 2002/0113466.
Instead of a corresponding movable mechanical connection, the attempt was made to connect the plastic cover by means of a material connection to the respective frame. For plastic covers using conventional materials, such as polycarbonates, to achieve the stability and durability of the cover required in motor vehicle construction, additional layers of hard material are applied to the outside and inside of the cover and are generally detrimental to a connection to other materials. As a result, the foaming-in-place processes used for glass covers to date are not applicable to plastic covers, and when a plastic cover is cemented to the frame, especially due to the aforementioned major differences with respect to coefficients of thermal expansion, faults and breaks in the cement often occur.